Android View中OnKeyListener的onKey返回值

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1. 前言

在调试Android原生Setting开始中，遇到DialogPreference中用遥控器操作SeekBar到100%时，再按一次右键SeekBar焦点会跳至确定按钮中去。正常现象应该是停留至SeekBar尾部。

2. 问题分析

根本原因就是焦点变化了，当SeekBar为100%时，再按一次右键让焦点停留再当前位置即可。
进一步分析就是对按键进行处理，当满足条件时，使系统不再处理这个按键。

3. 原生代码片段

在View.java中

    /** * Interface definition for a callback to be invoked when a hardware key event is * dispatched to this view. The callback will be invoked before the key event is * given to the view. This is only useful for hardware keyboards; a software input * method has no obligation to trigger this listener. */
    public interface OnKeyListener { 
   
        /** * Called when a hardware key is dispatched to a view. This allows listeners to * get a chance to respond before the target view. * <p>Key presses in software keyboards will generally NOT trigger this method, * although some may elect to do so in some situations. Do not assume a * software input method has to be key-based; even if it is, it may use key presses * in a different way than you expect, so there is no way to reliably catch soft * input key presses. * * @param v The view the key has been dispatched to. * @param keyCode The code for the physical key that was pressed * @param event The KeyEvent object containing full information about * the event. * @return True if the listener has consumed the event, false otherwise. */
        boolean onKey(View v, int keyCode, KeyEvent event);
    }

4. onKey返回值说明

由上面的代码可见，对按键监听时，onKey的返回值不同，代表对按键的不同处理方式。

false: 抛给系统处理 (将事件放行，焦点会移动)
true:  用户自己处理 (将事件拦截，焦点不会移动)

因此，当满足条件时，让onKey的返回值为true即可将键值拦截下来由用户自己处理，系统便不再响应这个按键，焦点便不会移动。